Due to their dimensions, wind turbine towers, in particular metal (e.g. steel) towers, are comprised of several tower sections or tower segments. A tower section is hereby referred to throughout this description as a part of a tower along the longitudinal extension of the tower, i.e. in an assembled state of the wind turbine along its extension from the ground to a nacelle (at which there is assembled the rotor of the wind turbine).
Tower shell parts in contrast are considered to be parts of the tower along its circumference. Often, a tower section comprises a plurality of shell parts. Therefore, to construct a tower, typically, first the shell parts have to be interconnected (for instance via adjacent vertically orientated inner flanges of the shell parts which are bolted together) to form a tower section and then the tower sections have to be placed on top of one another to form the tower. During that process they can again be bolted together via adjacent outer or inner (horizontal) flanges of two tower sections.
Such a wind turbine tower with sections and shell parts is for instance described in the international patent application WO 2009/097858 A1. The assembly of the tower can for instance be accomplished by means of an assembly rig such as then one described in the international patent application WO 2012/007226 A2.
During assembly of such tower sections on an assembly rig such as the one described in the above-given reference, there is currently a handling problem. The tower section can either be immediately lifted or raised and installed on top of the preceding tower section so as to form the tower or it needs to be stored temporarily on the ground until a sufficient raising or lifting means such as a crane is available to take it to its designated position on top of a preceding tower section.
In particular, the upper tower sections which are to be installed to form the top part of the tower (or a part slightly below that top part) require very tall and thus expensive cranes for installation. Thus, if all tower sections have to be transported right to their point of installation such crane must be available throughout the complete construction time of the tower. This implies a lot of waiting time of such cranes, which means a great waste of resources and expenditure.
The alternative to temporarily store the tower sections on the ground is presently not possible because there is a severe danger of injuring the tower section while placing them on the ground or during storage on the ground. In particular, the tower sections are normally delivered to the assembly site in such a state in which the tower shell parts have been interconnected in order to form the tower section and in which the tower section has been painted (at the manufacturer's site) with a finish, also on all of their distal edges. It is very important that the paint or finish stays intact after the installation of the tower section and thus during storage of the tower section.